With strong demand for larger data storage capacity in computers, data areal density in hard disk drive has increased significantly by about 30-40% per year. With the increase in data areal density, the intervals between data tracks are becoming narrower and narrower. The narrower data tracks make it difficult for hard drive motors to quickly and precisely position the read/write head over the desired tracks for data storage. Typical hard drive actuators such as voice coil motors (VCM) usually cannot meet the resolution and bandwidth requirements of high track density hard disk drives.
Great efforts have been made to increase the resolution and bandwidth by incorporating a second-stage actuator on the load beam of a head gimbal assembly or between the slider and the load beam. However, there are still difficulties in meeting the higher displacement resolution and broader bandwidth requirements of high track density hard disk drives (up to 1 to 10 TBit/in2).
For a second-stage actuator which is placed on the load beam, the displacement resolution and resonant frequency are not high enough for high track density hard drives, although it has a better performance than that without second-stage actuators.
For a second-stage actuator which is placed between the slider and the load beam, the fabrication process is usually complicated. For some types of micro-actuators, the precision of actuator dimensions may affect the displacement performance of the actuators, which makes it demanding for quality control during manufacturing. When the second stage actuator is a piezoelectric ceramic micro-actuator in shear mode, the resulting shear displacement under a typical 12 V working voltage cannot provide large enough displacement to drive the read/write head. Piezoelectric multilayer ceramic actuator in shear mode can provide larger displacements but the complicated structure significantly compromises the reliability of the actuator and increases the cost.